High Efficiency AAC aka HE-AAC aka aacPlus
aacPlus is a lossy data compression scheme for audio streams. It is based on MPEG-4, and combines three techniques: Advanced Audio Coding (AAC), Spectral Band Replication (SBR), and parametric stereo (PS).
aacPlus was standardized by the MPEG as part of the MPEG-4 Part 3 specification, under the High Efficiency AAC (HE-AAC) name.
For details on the MPEG-4 Part 3 specification, see wikipedia:MPEG-4_Part_3.
In HE-AAC, Spectral Band Replication (SBR) technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1 (HE-AAC v1), (sometimes known as aacPlus v1).
Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .
- .m4a file extension (the "mpeg4-audio" extenstion popularized by Apple iTunes)